Multiple bimetallic element



United States Patent MULTIPLE vBIMETALLIC ELEMENT Webley E. Barton, Staten Island, N.Y., assignor, by mesne assignments, to .Daystrom Incorporated, Murray Hill, N.J., a corporation of New Jersey Application August 7, 1956, Serial No. 602,574 .ltClaim. .(Cl. 13-363 This invention relates to bimetallic elements and particularly to coiled orhelical bimetallic elements for use in recording thermometers, thermal actuated switches and the like.

Helical coils which are formed from bimetallic strip material provide economical and relatively accnrate temperature sensing elements for a variety of'uses. The amount of deflection which is obtained with a single helical bimetallic element, for a given increment in temperature, is a direct function of the'length of the bimetallic strip used in making the helix. If, for example, the length of the bimetallic element strip is increased, and all other factors remain the same, the deflection of the strip increases, for a given increase in temperature. That is to say, the deflection rate increases with increased length. On the other hand, the torque which a bimetallic helix produces is a direct function of the cross sectional area of the component metals which make up the bimetallic strip. If the cross section of the metals is in.- creased, and all other factors remain the same, the torque of the element increases, for a given change in temperature. The torque produced by ordinary bimetallic coil is relatively small, and it would at first appear that a simple method of increasing the torque would be to increase the cross sectional area. of the bimetallic element. However, increasing the cross section results in a decreased deflection rate. It is seen then, that in order to increase the torque by increasing the cross sectional area of the bimetallic strip, and at the time maintain the same deflection rate, the length of the strip must be increased. Lengthening of the bimetallic strip, however, requires a greater space thereby resnlting in 'a bulky apparatus. Also, the increased length reduces the rigidity of the bimetallic helix thereby resulting in a device which is susceptible to shock and vibration.

An object of this invention is the provision of a thermally responsive device, including a plurality of bimetallic helical elements, which produces greater torque and which possesses greater rigidity than a single bimetallic helix of the same size and same deflection rate.

An object of this invention is the provision of a temperature responsive device which includes a plurality of concentric bimetallic coils fastened together at their ends.

An object of this invention is the provision of a temperature responsive system including at least two coaxial bimetallic coils that are mechanically connected at both ends whereby the deflection rate of the system is substantially the same as the deflection rate of the individual coils and the combined torque is substantially increased over the torque of any of the individual coils.

An object of this invention is the provision of a temperature responsive device comprising a plurality of concentric helical coils of bimetallic strip wound in the same sense and with the component metals of the strip material similarly arranged in the said coils, a supporting member for supporting one end of each of the said g 2,918, 820 Paten e n 952 2 helical coils, and means fastening the other end of each helical coil together.

These and other objects and advantages will beco e apparent from the following description when taken with the accompanying drawings. It will be understood, how; ever, that the drawings are for purposes of llustration and are not to be construed as defining the scope or limits of the invention, reference being had for the latter purpose to the appended claim.

In the drawings wherein like reference characters denote like parts in the several views:

Figure l is a front view of a pair of helical bimetallic coils in a disassembled relationship;

Figure 2 is a front view of the two helical bimetallic coils concentrically positioned and showing a portion of the coils broken away; and l v Figure 3 is a more or less diagrammatic presentation, with parts broken away, of a recording thermometer wherein my novel thermal responsive device is embed Referring to Figure 1 of the drawings, reference numeral 10 identifies a helical coil of bimetallic strip ma,- terial which comprises component metal layers 11 and 12, as is well understood. The bimetallic strip material may be wound with the metal having the greatest co eflicient of expansion on either the inside or outsid the coil. A helical coil 15 is similar in shape and s ze to the helical coil 10 and comprises similar component metal layers 16 and 17 which are arranged in the same relative manner as the layers 11 and 12 of the helical coil v1t It will be understood that helical bimetallic I coils are often manufactured in long lengths and, in practice, the helical coils 10 and 15 may be sections of coil which are cut from the original coil, in which case they would be of substantially identical diameter and exhibit substantially identical properties,

Reference is now made to Figure 2 of the drawings wherein the two helical coils 10 and 15 are shown arranged concentrically, with the coil 15 inside the coil 10. The coils are easily compressed and expanded man; ually making it a simple process to insert the coil 15 within the coil 10. This may be done, for example, compressing the coil 15 slightly and turning it into the coil 10. When one end of each of the coils are brought into alignment as indicated at reference numeral other end of the inner coil 15 will extend beyond end 9 he ou r coi ,10 a t 23 and thi p 23 may be cut off or removed, if desired. Holes 20 aiid 21 are drilled, or otherwise suitably formed, through both of the coils 10 and 15 at both ends thereof. The holes provide means whereby the two coils may be fastened together, as by rivets or bolts; and at the same time provide means whereby the coils may be suitably secured to a supporting member at one end thereof. An actuated member, such as a recording pen or switch arm, may be secured to the other end of the coils by use of suitable fastening means through the hole thereat. The two bimetallic helices must not be joined or secured together along their entire lengths; only the adjacent ends are held securely relative to each other.

If the two unassembled coils 10' and 15, as shown in Figure l, are identical so that the deflection rate of both coils is the same when the coils are unassembled, then the deflection rate of the two assembled coils, as shown in Figure 2, will be slightly less than that of either unassembled coil alone because the short length 23 of the inner coil 15 is unused; and, as suggested above, may be removed or cut off. For ordinary use the deflection rate of the assembled coils is so near to that of each of the unassembled coils that it may, for many practical purposes, be considered to be the same.

It has been found, however, that even when the two coils and of Figure l, are cut from the same original coil that, due to manufacturing tolerances, the deflection rate of the two coils may differ slightly. If desired, a double helix construction which has a deflection rate which is very near the deflection rate of the coil having the lowest deflection rate may be constructed. This is done by selecting the coils such that the inner coil 15 has a higher deflection rate than the outer coil 10 by such an amount as to make the deflection rates equal when the coils are assembled and the protruding end piece 23 is left unused or cut off.

It will be understood that this refinement in the selection of the coils is generally not essential in the manufacture of the ordinary thermal responsive device. The proper deflection rate may be easily obtained by cutting the assembled coils to the proper length.

Reference is now made to Figure 3 of the drawings wherein my novel multiple bimetallic helical thermal sensing element is shown embodied in a recording thermometer. The recording thermometer comprises a rear mounting plate 25 having a plurality of internally threaded extending lugs 26 suitably fastened thereto. A front mounting plate 27 is mounted on the extending lugs 26 by use of screws 28 which extend through holes in the front mounting plate, and threadedly engage the lugs 26. A spring, electric, or other suitable motor 29 is mounted between the rear and front mounting plates 25 and 27, respectively. A threaded motor shaft 30 extends through a hole in the front mounting plate; and a temperature chart 32, made of paper or other suitable material, is suitably fastened thereto as by a nut 33.

My novel multiple bimetallic helix (comprising the supporting member 34, which extends inwardly from the rear mounting plate 25. A screw 35, which extends through the hole 20' in the multiple bimetallic helix and engages a threaded hole in the supporting member 34, secures the multiple bimetallic helix to the supporting member 34 and at the same time holds the ends of the coils 10 and 15 together. The other end of the multiple bimetallic helix is free to rotate with changes in temperature and supports a pen 37 attached thereto as by a rivet 38, for example, which extends through the hole 21' in the end of the multiple bimetallic helix and the hole in the pen arm. At the same time, the rivet 38 holds the free ends of the individual coils 10 and 15' together. It will be understood that a time record of temperature is made on the temperature chart 32 by the pen 37 as the chart is made to rotate by action of the motor 29. The chart may be calibrated in temperature .coils 10' and 15) is mounted on a cylindrical shaped values and time of day as shown. In Figure 3 of the drawings, the multiple bimetal'helix is wound such that the low end of the pen arm 37, as viewed in the drawing, rotates to the left and upwardly with an increase in temperature.

If only one bimetallic coil is used in such a recording thermometer (as is common practice), the torque which is produced by the single coil is small and, because of surface roughness of the chart 32, the pen may stick on the chart thereby resulting in an inaccurate temperature record. By using the multiple bimetallic helix of my invention the torque produced is increased (approximately doubled if a tWo coil bimetallic helical system is used) with substantially no change in the deflection rate of the element and with no increase in space necessary to house the device. In addition, the two coil system is much more rigid than a one coil system and will stand more shock and rough handling.

It will be understood that my invention is not limited to the use of only two concentric bimetallic helices. Three or more bimetallic coils may be concentrically arranged in the same manner and secured together at their ends so that the torque is increased approximately 3 or more times that of a single coil system, depending on the number of coils used. Such multiple bimetallic helices are well adapted to actuate switches and recording pens and other devices wherein a relatively large torque is necessary for reliable operation.

Having now described my invention in detail in accordance with the patent statutes, various changes and modifications will suggest themselves to those skilled in this art, and it is intended'that such changes and modifications shall fall Within the spirit and scope of theinvention as recited in the following claim.

I claim:

A thermally responsive element comprising a pair of bimetallic coils initially of the same size, and inserted one within the other, with the turns of the outer coil covering those of the inner coil and with the inner surface of said outer coil directly engaging the outer surface of the inner coil, said inner coil having a higher thermal deflection rate than the outer coil by such an amount as to make the thermal deflection rates equal, when said coils are so assembled, and means fastening the adjacent ends of said coils directly together at both ends thereof.

McWilliams Mar. 31, 1936 Howard July 27, 1943 

